VRE Colonization and Infection

Antibiotic-resistant bacteria are an increasing problem in hospitalized patients and commonly cause infections following broad-spectrum antibiotic administration. Among these, Vancomycin-resistant Enterococcus (VRE) is one of the most common causes of bloodstream infections. Commensal microbes that colonize mucosal surfaces provide defense against infection by physically occupying niches and competing for nutrients. In addition, commensal microbes also condition the intestinal mucosa to resist bacterial invasion by inducing expression of antimicrobial molecules. Clinical use of antibiotics profoundly alters the commensal flora by killing subsets of microbes that are normal intestinal inhabitants. The downstream effects of antibiotic-induced microbial depletion on mucosal innate immune defenses include decreased expression of RegIIIγ, a bactericidal C-type lectin that is secreted by intestinal epithelial cells. RegIIIγ kills VRE in the ileum of mice and decreased expression of RegIIIγ during antibiotic treatment increases susceptibility to VRE colonization (Figure 1).  Our laboratory has demonstrated that oral administration of lipopolysaccharide (LPS), a ligand for TLR4, or systemic administration of flagellin, a ligand for TLR5, reverses antibiotic-induced down-regulation of RegIIIγ and enhances resistance to colonization with VRE (Figure 2).

To begin to define the commensal bacterial species that confer resistance to VRE colonization, we transplanted fecal microbiota from antibiotic-naïve mice to mice that had intestinal domination by VRE. 

Figure 3

Figure 3: Fecal transplantation eliminates VRE from the gastrointestinal tract. Mice were treated with ampicillin and then inoculated with VRE. On day 1, mice were either transplanted with fecal microbiota from an antibiotic-naïve mouse (red dots labeled Fecal Pellet) or treated with PBS (blue dots). Over the course of 14 days, mice transplanted with a normal microbiota eliminated VRE from their colons (Ubeda et al. Infection and Immunity, 2013).

In order to begin to associate specific bacterial species with clearance of VRE from the gut, we reconstituted mice with fractionated fecal microbiota obtained from antibiotic-naïve mice and correlated microbiota composition, determined by next generation sequencing of 16S rRNA genes, with clearance of VRE.  Figure 4 demonstrates that the presence of Barnesiella in the colon correlates with resistance to VRE colonization of the gut.

Figure 4

Figure 4: Mice were reconstituted with fractionated microbiota and resistance to VRE colonization was determined. Each horizontal line represents an individual mouse, and mice are ranked from top to bottom from lowest to highest resistance to VRE (blue heat map on right). The relative frequency of different bacterial taxa is shown in the heat map by shades of red (Ubeda et al. Infection and Immunity, 2013).

Ongoing studies in our laboratory are focusing on the development of bacterial consortia that provide high-level resistance to VRE, and to determine mechanisms of microbiota-mediated resistance to VRE colonization beyond the role of RegIIIγ.

Brandl K, Plitas G, Mihu CN, Ubeda C, Jia T, Fleisher M, Schnabl B, DeMatteo RP, Pamer EG. Vancomycin-resistant enterococci exploit innate immune deficits induced by antibiotic treatment. Nature. 2008; 455(7214):804-807.

Kinnebrew MA, Ubeda C, Zenewicz LA, Smith N, Flavell RA, Pamer EG. Bacterial flagellin stimulates TLR5-dependent defense against vancomycin-resistant Enterococcus infection. J Infect Dis. 2010 Feb 15;201(4):534-43.

Ubeda C, Taur Y, Jenq RR, Equinda MJ, Son T, Samstein M, Viale A, Socci ND, van den Brink MR, Kamboj M, Pamer EG. Vancomycin-resistant Enterococcus domination of intestinal microbiota is enabled by antibiotic treatment in mice and precedes bloodstream invasion in humans. J Clin Invest. 2010 Dec 1;120(12):4332-41.

Kinnebrew, MA, Buffie, CG, Diehl, GE, Zenewicz, LA, Leiner, I, Hohl, TM, Flavell, RA, Littman, DR, Pamer EG. IL-23 production by intestinal CD103+CD11b+ dendritic cells in response to bacterial flagellin enhances mucosal innate immune defense. Immunity. 2012 Feb 24;36(2):276-87.

Ubeda C, Lipuma L, Gobourne A, Viale A, Leiner I, Equinda M, Khanin R, Pamer EG. Familial transmission rather than defective innate immunity shapes the distinct intestinal microbiota of TLR-deficient mice. J Exp Med. 2012 Jul 30;209(8): 1445-56.

Ubeda C, Bucci V, Caballero S, Djukovic A, Toussaint NC, Equinda M, Lipuma L, Ling L, Gobourne A, No D, Taur Y, Jenq RR, van den Brink MR, Xavier JB, Pamer EG. Intestinal microbiota containing Barnesiella species cures vancomycin-resistant Enterococcus faecium colonization. Infect Immun. 2013 Jan 14.